The present invention relates to a linear hydraulic pivot drive.
Linear drives of this type are used, for example, for the flap control of aerodynamic profiles. Here, it is particularly advantageous that conventional rod linkages or control rods can be eliminated which are pivotally connected to the control flap outside the aerodynamic profile and thus have a negative influence on the aerodynamic conditions.
A known drive for controlling a rotor blade aileron is described, for example, in British Patent Document GB 2 299 562 A. For converting a hydraulically caused axial movement of a shaft to a rotational movement, the shaft is provided with a coarse thread. The coarse thread engages in several bushes which concentrically surround the shaft, so that the bushes undergo a rotation during the axial displacement of the shaft. In this case, a torque support of the shaft is required in order to effectively prevent its rotation. This is caused by an additional mechanism which secures the shaft. The mechanism comprises several components; among others, separate bores into which the shaft is introduced, as well as detent pins. This type of an arrangement not only has relatively large dimensions but also causes intensive mounting and maintenance work.
In addition, so-called coarse-thread swivel motors are known which convert an axial displacement of a hydraulic working piston by way of coarse threads to a rotational movement of an output shaft. The torque support of the working piston takes place, for example, by two threads which extend in opposite directions and which engage in the piston on both sides. However, this results in an opposite rotating direction of the output shaft, which is undesirable for some applications. In addition to being arranged axially behind one another, the threads can also be arranged in a radially nesting manner. In this case, particularly because of the not arbitrarily reducible pitch of the coarse threads, an arbitrary reduction of the arrangement cannot be achieved. Therefore, commercial drives, as a rule, are relatively large. It is also disadvantageous that, in the case of such conventional hydraulic pivot drives, there is a concentration on spot-type load distributions.
Recently, aerodynamic structures have been developed which have smaller flap arrangements (so-called miniflaps), which differ from conventional flaps with a 10–30% clean wing depth in that they have a depth of only 1–3% and, as in the case of a split flap, consist of a stationary and of a swung-out part. An aerodynamic profile with such a miniflap is described, for example, in our unpublished Patent Application DE 101 56 733 (corresponding U.S. 2003/102410). A deflection of the miniflap by means of conventional adjusting levers would not only cause unfavorable flow conditions but also result in a high weight since several adjusting levers would be required. Likewise, high mounting as well as maintenance expenditures would be necessary.
New actuator systems are therefore required which, in particular, meet the demands of a high miniaturization. Because of the structural demands, only a very limited installation space is available. The flap actuator system should be aimed at a greater integration of the functional tasks of the drive and the bearing structure. In addition, a linear or plane distribution of force or power is desirable in order to meet the flap-specific demands.
It is therefore an object of the present invention to create a linear hydraulic pivot drive which has a small size as well as a simple construction, so that it can be integrated in existing structures and requires low maintenance expenditures.
This object is achieved by means of a linear hydraulic pivot drive which comprises a housing with connections for introducing a hydraulic medium, a piston arranged inside the housing, which piston is axially displaceable by the action of the hydraulic medium, as well as an output shaft provided with coarse threads, which output shaft interacts with the piston in order to convert the axial movement of the piston to a rotational movement, and, according to the invention, is characterized in that the output shaft is integrated in the piston, the coarse threads being constructed to run in the same direction and engaging in the piston, and in that the piston cross-section has a spline profile in order to effectively prevent a rotational movement of the piston.
By constructing the piston cross-section in the form of a spline profile, the torque support for preventing a rotation of the piston is ensured by the latter itself. Expediently, the spline profile is provided in the engaging area of the output shaft and the piston; that is, in the cross-sectional area of the piston where the mutual engagement of the output shaft and the piston takes place. As an alternative, the spline profile may be constructed along the entire piston. The spline profile preferably is a P4C-profile according to DIN Standard 32712. Here, it is particularly advantageous that the axial displaceability is ensured under the force of moments. In this manner, no additional mechanisms and components are required in order to prevent a rotation of the piston. A simple construction is ensured. Furthermore, it is advantageous that, as a result of such a design, the pivot drive is significantly smaller than known arrangements. It is particularly expedient in this case that the output shaft is integrated in the piston on both sides.
It is particularly advantageous that the output shaft has two separate sections at whose respective ends engaging in the piston the coarse threads are arranged which run in the same direction. In this manner, it is achieved that the rotating direction of the output shaft sections is identical.
The output shaft sections are preferably mutually connected in a rotationally symmetrical manner by way of a spacing pin, the spacing pin being introduced into respective bores provided in the output shaft sections. This is advantageous particularly with respect to the mounting as well as the maintenance.
Expediently, the piston is equipped with threaded bushes on both sides, the coarse threads of the output shaft sections engaging in these bushes. As mentioned above, in this manner a uniform rotating direction of the output shaft sections is obtained. This also ensures a force transmission which is as high as possible.
Further, it is advantageous that the piston has a central bore, the spacing pin extending through this central bore. The spacing pin is thereby disposed in a simple manner. For this purpose, a bearing may be arranged in the central bore.
Expediently, axial-radial bearings, preferably roller bearings, are provided for the bearing of the output shaft. As an alternative, the axial and radial components may also be constructed separately. These bearings permit a good absorption of axial as well as of radial forces.
It is particularly advantageous to integrate the axial-radial bearings in housing covers which, in turn, tightly close off the housing. This advantageously results in a compact type of construction.
Furthermore, it is expedient that the hydraulic medium can be bidirectionally introduced into the housing, which permits a swivelling of a flap, which is pivotally linked to the housing, in different directions.
The pivot drive according to the invention is used particularly for the flap deflection at rotor blades or airplane wings. In this case, it is particularly advantageous to integrate the drive in a hinge joint of a flap hinged to an aerodynamic profile, a plurality of such drives being linearly integrated in the hinge joint.
In the following, the invention will be explained in detail by means of the attached drawings.